What is Dolby Atmos For Home Theater?

Two years ago, Dolby Atmos hit the commercial theater scene with the promise of a more enveloping, and consequently more lifelike sound. The most noticeable aspect of the format was the addition of more speakers, with up to 64 channels of audio supported, including ceiling mounted speakers for overhead effects. However, the extra channels are just the beginning: as we noted in Dolby Atmos for Home Cinema, Dolby Atmos utilizes three distinct elements:

• Bed Audio: these are channel-based stems, in 5.1 or 7.1, effectively identical to former surround-formats. The individual channels are static inside the bed.
• Object Audio: these are mono- or stereo channels with dedicated surround panning. These channels are not in a bed, but remain individual.
• Metadata: Surround panner metadata for Object audio and additional metadata
  

“Objects” can be surround panned in space on all three axes (front/rear, left/right, up/down), as well as given a size. The Metadata defines where the objects are positioned and how big they are in time. In a normal surround environment, these surround pans are transformed to output levels in the classic 7.1 mix channels. Conversely, objects are “rendered” by the Atmos engine; up to 128 different elements (9.1 bed channels plus 118 objects) can be rendered to the actual number of speakers the system has available, up to a maximum of 64 individual speaker feeds in a commercial cinema.

Illustration of object audio in Dolby Atmos.

The end result of all this is a more involving and pinpoint accurate experience than conventional 5.1 or 7.1 could ever offer. Instead of effects simply appearing behind or beside you, Atmos delivers a three dimensional reproduction of effects such as an airplane flying overhead, the utter sonic immersion of being in a jungle, or something as simple as the rain falling.

What is Dolby Atmos for Home Theater?

Bringing It Home

If you’ve been following the flurry of manufacturer announcements lately, Atmos isn’t just for commercial theaters anymore. D&M announced new A/V receivers from both Denon and Marantz supporting the format, as have Yamaha, Onkyo/Integra, and Pioneer. At the same time, Pioneer has launched a new line of “Atmos-enabled” speakers with other manufacturers sure to follow suit. All of this raises an important question: what exactly do you need to enjoy the benefits of Dolby Atmos at home?

Dolby Atmos: what the numbers mean.

Before answering that question, it’s important to understand how Atmos will be delivered in the home. Atmos content will not require a new codec. Instead, it will take the form of extensions within the current Dolby TrueHD and Dolby Digital Plus codecs. As such, while you will need a new A/V receiver to take advantage of these extensions (older models will simply play the base TrueHD/Digital Plus content), Blu-ray players that fully conform to the Blu-ray specification will support Atmos without requiring a firmware update. Moreover, despite what cable salesmen might state in the future, you don’t need new HDMI cables either.     

What about the speakers? Atmos in the home supports up to 24 speakers on the floor and 10 overhead speakers (34 speakers total), and Dolby has noted that one partner is already planning on releasing a 32 channel A/V receiver to take advantage of this expandability. However, you don’t need a room full of speakers to benefit from Atmos. Currently, the options are largely limited to 11.1 channels of audio, with a few different configurations options to consider.

Dolby Atmos Speaker Configuration Options for Home Theater

• 5.1.2: A standard 5.1 setup with a pair of “middle” in-ceiling/ceiling-mounted speakers.
• 5.1.4: A standard 5.1 setup with a front and rear pairs of in-ceiling/ceiling-mounted speakers.
• 7.1.2: A standard 7.1 setup with a pair of “middle” in-ceiling/ceiling-mounted speakers.
• 7.1.4: A standard 7.1 setup with a front and rear pairs of in-ceiling/ceiling-mounted speakers.
• 9.1.2: A 9.1 setup utilizing front wide channels and a pair of “middle” in-ceiling/ceiling-mounted speakers.

Diagrams of all the supported Dolby Atmos configurations using 7.1 through 11.1 channels. Images sourced from Dolby.

Looking at the diagrams, it’s worth noting that Atmos ceiling speakers are located a bit differently from the old front/rear height speakers in current expanded Dolby PLIIz 7.1 or 9.1 setups.  X.X.2 and X.X.4 Atmos setups both utilize in-ceiling speakers located towards the middle of the room, vs. the old wall mounted height channels. As such, consumers wishing to repurpose hardware for a new Atmos home theater may need to reposition their speakers accordingly for the best results. Of course as you might guess, the most convincing effects will come from the X.X.4 systems, which will allow for better front to rear panning of sound effects. However, Dolby is confident that even the X.X.2 setups will yield a significant improvement over non-Atmos configurations.

In-Ceiling vs Atmos-Enabled Reflective Speaker Technology

In addition to the number of channels, there’s also the question of whether you wish to utilize discrete in-ceiling/ceiling-mounted speakers or “Atmos-enabled” speakers utilizing what they call reflective speaker technology. The latter option (of which the aforementioned Pioneer Elite Speakers are an example) adds a separate driver array which is aimed toward your ceiling. The drivers are band limited, and special processing takes place within the Atmos engine to alter select frequencies in order to create the psychoacoustic effect of sound appearing to come from above you. Dolby notes that Atmos-enabled speakers do not rely on virtualized processing like a soundbar, which also means there’s NOT a narrow sweet spot to get the "Atmos" effect.  This is claim is very curious and we look forward to verifying ourselves. 

Dolby Atmos Speaker - notice the separate connections for the front or rear main channel and the new Atmos height channel.

Shown above is a generic diagram of a typical Atmos-enabled speaker proposed by Dolby.  Notice the driver is recessed into the baffle.  We can't help but wonder how they are dealing with diffraction issues caused by this approach so it will be interesting to pull some measurements once review samples become available.  We also have to ponder how the added mechanical vibrations from a separate speaker integrated into a shared cabinet will affect the overall sound quality of the main or rear channels.

Some manufacturers will be offering Atmos speaker add-on modules to place on-top of your current front and/or rear speakers like this example below from Onkyo.

Onkyo SKH-410 Atmos Speaker Add-On Module

Of course there are important caveats to consider on both sides of the equation. In-ceiling speakers are relatively easy to localize if you’ve got low ceilings (say 8’), taking away from the immersive effect. Conversely, Atmos-enabled speakers are best suited for ceiling heights of 8-9 feet. While Atmos-enabled speakers can work with ceilings as high as 14 feet, Dolby states that the effect does become more diffuse. In addition, your ceiling should be a flat surface (i.e. not vaulted/angled), and be made of an acoustically reflective material such as drywall, concrete, or wood for best results with Atmos-enabled speakers. We’ve also heard that most A/V receivers will require you to specifically select an “Atmos-enabled speakers” option to correctly compensate for sound propagation delays.

5.1.2 and 5.1.4 configurations using Atmos enabled speakers. Image sourced from Dolby. Users wishing to implement a 5.1.2 setup without in-ceiling speakers should utilize Atmos enabled front L/R speakers. Note that this suggests a different "virtual placement" vs. the centrally placed in-ceiling X.X.2 in-ceiling speakers.

Atmos Surround Upmixing: Going Beyond Prologic IIz

Now it’s all fine and good that you can enjoy Atmos with future releases, but a lot of folks already own a pretty sizeable collection of films. What’s in it for them you ask? As it turns out, the Atmos engine also includes a surround upmixer, which replaces the Dolby Pro Logic II family of upmixers. As you might imagine, the Atmos upmixer is a bit more advanced than previous generations. The Atmos engine starts by performs a granular analysis of legacy sources, which can range from good old two channel content to the latest 7.1 Dolby TrueHD mix. From there, the system is capable of steering individual frequency bands from each channel to create up to a 24.1.10 matrixed Atmos environment. Of note: the Atmos upmixer will not send redirected content to speakers between the front left, center, and right speakers in order to minimize the impact on the front stage.

Summary

Ready or not, the market is about to be flooded with Dolby Atmos related gear. To take advantage of the new format, consumers will need to make a significant investment: in addition to new speakers, be they in-ceiling/ceiling-mounted models or Atmos-enabled, you will also need to purchase a new A/V receiver. It’s not hard to see the importance of this to the industry; in the face of declining AV receiver sales, a new theater format which can make use of up to 11 channels of audio is of great benefit to manufacturers, retailers, and installers. Moreover, Dolby Atmos greatly simplifies the creation of movie soundtracks for producers; only a single master mix is required to support all speaker configurations/layouts. So what’s in it for us?  Dolby merely promises the most immersive audio experience yet. Only one question remains: are you ready for Atmos?

Article updated on 8/9/2014 due to the recent release of Dolby's Atmos for the Home Theater whitepaper.